Some version of BIOS does not enable all clock levels,
resulting in high level clock frequency of 0.
The number of valid CLKs must be confirmed in advance.
Signed-off-by: Peyton Lee <peytolee@amd.com>
Reviewed-by: Lang Yu <lang.yu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>